A biological photometric device is capable of measuring blood circulation, hemodynamics or variation of hemoglobin quantity in a living body in a simple manner without much restriction or any harm to the body, by irradiating light within the range from a visible light to infrared light to the living body of an object to be examined, and detecting the reflected light and scattered light passed inside of the living body.
The biological photometric device is used, for example, when a head region is the subject for measurement, for identifying activated state of the brain due to hemoglobin alteration in blood inflowing in a blood vessel in the brain upon physiological stimulation being imparted, or local focus of epileptic seizure, etc.
In Non-patent Document 1, measurement of hemoglobin alteration in a brain upon performing motion/language task, by cerebral blood flow mapping method using near infrared ray is reported. According to the report, it is disclosed that hemoglobin increment in the brain acquired by physiological stimulation such as motion/language task performance is only 5% at the most. This is also confirmed by other measurement methods such as PET (Positron-Emission Tomography).
While variation of hemoglobin amount in the brain due to physiological stimulation amounts to 5% at the most, noise signals measured by a biological photometric device often turn out to be a considerably large value of more than 50% when they are converted into the amount of hemoglobin variation in the brain. Hardly any signals indicating the amount variation of blood accompanying brain function activities are included in these noise signals, and they become a major diagnostic impediment.
In Patent Document 1, a method is described for detecting and eliminating spiky noise signals attributed to gaps generated in the very short period of time between an object and an aperture of optical fibers (hereinafter referred to as spike noise signals) by factors such as displacement of the applied light irradiating unit and light detecting unit. Discrimination between spike noise signals and normal signals is performed by determining whether derivative value of signal intensity is more than a predetermined threshold value or not.
Patent Document 1: WO 03/002004
Non-Patent Document 1: CLINICAL NEUROSCIENCE Vol. 17, No. 11, 1999-11